The present invention relates to an improved apparatus and improved method for retrieving objects from a well bore.
Diesel, solar and wind powered water wells are often used where it is difficult or expensive to provide electrical power. While solar power and windmills can be operated to generate electricity for an electric pump, the most common type of pump used with such water wells is a positive displacement cylinder pump. A positive displacement cylinder pump is driven by a reciprocating rod connected, for example, to a gear box at the windmill rotor.
Generally, any mechanism that seals water in a chamber and then forces it out by reducing the volume of the chamber can be considered a positive displacement pump. Piston, or plunger pumps are reciprocating pumps that use a piston or plunger to move the water through a cylindrical chamber. When such pumps are used in a well bore, the cylinder and piston are positioned below the water table in the well bore, and water must flow into the well bore from below the cylinder. When the piston moves up, a bottom, or lower check valve allows water to flow into the cylinder. When the piston moves down, the bottom check valve closes and water is forced through an upper, or top check valve to the surface.
Many repairs required in wells that use positive displacement pumps are due to debris in the cylinder or “working barrel” of the pump. The debris can be foreign material entering the well from the surface or silt and sand entering from the subterranean formation. The debris can also be worn rings, seals, sleeves, or other material from the pump itself. Whatever the source, the debris can jam the plunger in the cylinder and can also plug the opening of one of the check valves, which makes it impossible to close or open the valve and operate the pump efficiently. The plugging debris must be removed to restore operability to the pump.
Raising the plunger and upper check valve does not generally present a problem since both are already connected to the surface by the plunger rod. The plunger and upper check valve can be repaired or replaced on the surface and positioned back in the well. However, removal of the plugging debris requires pulling the pipe string, and this is a major cost.
Because the lower check valve is not connected to the plunger rod, it will generally remain in place. Check valves used in displacement pumps have an internally and externally threaded neck at the top thereof (the part facing up when placed in the well bore). The most commonly used check valves are ball type and spool type check valves. When the bottom check valve becomes plugged, it will either not close properly or not open properly. If the check valve cannot close completely, the plunger will displace water back to the formation rather than to the surface. If the check valve cannot open completely, water will not enter the well at the desired rate from the reservoir. Thus, when the bottom check valve is plugged, it must in many cases be removed. Because of the difficulty and high cost to remove the bottom check valve, such wells are often abandoned.
In some circumstances, the bottom check valve can be removed using a threaded tool at the end of a rod to threadedly engage the threaded valve neck. To remove the bottom check valve, the threaded tool must be rotated into the bottom check valve. In many wells this is very risky, in that the torsion required to thread the tool into the bottom check valve can cause the rod to break. Retrieval of the bottom check valve is made more difficult if any silt or other material is on the surface of the inner threads of the valve neck. Additionally, if the bottom check valve is not properly aligned vertically within the well, it is very difficult, and may be impossible, to thread the threaded tool into the check valve.
There is a need for a tool which will enable efficient removal of the lower, or bottom check valve from a water well, thus reducing repair costs and extending the life of the well.